1. Field of the Invention
The present invention relates to a disc drive used as an external storage device for an office automation machine, a personal computer and so on, and in particular, this invention is directed to a disc drive which has a restriction mechanism for restricting the location of a movable member to a designated position. The restriction mechanism restricts the movable member, such as a swing arm for supporting a head for reading and writing information in the disc drive when the electric power supply to the disc drive is interrupted and the disc drive is transported.
2. Description of the Prior Art
A requirement of portability for office automation machines and personal computers has recently emerged. Lap-top machines are good examples of answers to this requirement. In accordance with this trend in such computer systems, a disc drive, which is installed inside or connected outside a computer or office automation machine, needs to be provided with a structure for coping with vibrations and shocks during transportation of the disc drive in addition to having a mass-storage capability and short access time.
In a prior art disc drive comprising a well-known structure for coping with vibration and shock when the disc drive is out of service, a head for reading and writing information on a disc is moved to and restricted at a shipping position where no information is recorded on the disc. The disc drive is, however, subjected to a large number amount of vibrations and shocks during transportation of the disc drive. Accordingly, there may be a case in which the restriction mechanism fails to lock the head at a designated shipping position so that the head collides with and scratches the surface of the disc. As for a fixed disc drive having a head which is floated on the surface of the disc by the force of air caused by rotation of the disc, the head makes contact with the surface of the disc while the fixed disc drive is out of service or in transportation. If the head is released from the restricting mechanism when the fixed disc drive is out of service or in transportation, and the head is moved from the restriction position, the surface of the disc may be damaged as a result of being scratched by the head.
In order to establish a small-sized disc drive having a lightweight and which provides a high speed access, a recent type of disc drive often uses a mechanism in which the head is supported by a swing arm and a voice coil motor moves the swing arm. This mechanism takes advantage-of lower mechanical friction and higher precision in positioning the head on the disc. On the other hand, the restricting mechanism of the swing arm tends to be subjected to a small amount of vibration and shock applied to the disc drive, so that the arm is released from the restricting mechanism.
In some prior art disc drives, there are various kinds of structures and mechanisms for restricting the head at a designated position when the disc drive is out of service, handled in transportation or used during an unexpected loss of the electric power source. Now referring to FIGS. 1A, 1B and 1C, some examples of these prior art disc drives will be described. FIGS. 1A, 1B and 1C refer to fixed disc drives in which a disc 1 is driven at a constant rotational speed by an outer-rotor-type spindle motor 2 mounted on a case 6 of the disc drive. A head 3 for reading and writing information on a track zone TZ of the surface of the disc 1 is supported by one end of a swing arm 4 as a movable member. The arm 4 is rotating around a pivot axis 4p provided on the case 6. An actuator 5 for moving the arm 4 and locating the head 3 on the disc 1 is composed of a voice coil motor. The voice coil motor is composed of a fixed part 5a fixed to the case 6 and a movable part 5b which is formed by a voice coil and attached to the other end of the arm 4. A restriction mechanism of the arm 4 fixes the head 3 on a shipping zone SZ which is ordinarily formed at the inner region of the surface of the disc 1, when the disc drive is out of service and so on.
In the prior art disc drive shown in FIG. 1A, the restriction device has a coil spring 31 extended between a predetermined position on the side of the head 3 of the pivot axis 4p on the arm 4 and a support member 6a provided on the case 6. During operation of the disc drive, the actuator 5 applies a force against the coil spring 31 and moves the arm 4 in order to locate the head 3 within the track zone TZ. When the disc drive is out of service or used during an unexpected loss of the electric power supply, the electric power supply to the actuator 5 is also lost and the actuator 5 is inactivated, and then the arm 4 rotates counterclockwise due to the tension force by the coil spring 31 and a portion of the arm 4 collides with a stopper 4a. At this point, the arm 4 is stopped and the head 3 is fixed at the shipping zone SZ.
In the prior art disc drive shown in FIG. 1B, the restriction device has an electromagnet operator 32 on the case 6 and a linking portion 33 provided on the arm 4. In order to move the head 3 to the shipping zone SZ when the electric power supply to the actuator 5 is lost, by counter electromotive force of inertially rotating spindle motor 2, the actuator 5 is driven to move the arm 4 until it contacts the stopper 4a. As a result, a linking portion 32a of the electromagnet operator 32 and the linking portion 33 are linked to each other and the head 3 can be fixed in the shipping zone SZ.
In the prior art disc drive shown in FIG. 1C, a permanent magnet 34 fixed to the case 6 attracts a piece of magnetic substance 35 mounted on the arm 4 so that the head 3 can be fixed in the shipping zone SZ. In the same manner as the disc drive of FIG. 1B, the actuator 5 is driven to move the arm 4 to the fixed position by use of generated electric power by inertially rotating spindle motor 2 after loss of the electric power supply. In this example, the permanent magnet 34 is used also as a stopper. Thus, the permanent magnet 34 is supported by a support member 37 fixed to the case 6 through an elastic member 36 composed of a material such as rubber.
There are, however, some problems in the above mentioned prior art disc drives.
More specifically, in the example shown in FIG. 1A, in order to place the head 3 within the track zone TZ while operating the disc drive, it is required to supply electric power to the actuator 5 so as to generate enough torque to balance the tension force of the coil spring 31. This leads to a problem in that the power consumption of the disc drive increases. Additionally, since the arm 4 is only fixed by the force generated by the coil spring 31, the head 3 is apt to vibrate when a relatively large force is applied to the arm 4. Increase the tension force of the coil spring 31 in order to reduce the vibrating effect leads to an increase in power consumption.
In the example shown in FIG. 1B, although the problem relating to power consumption occurring in the previous example is not present, there is a problem with mechanical friction between the linking part 32a and the linking part 33. This means that alternating between a restriction work mode and a release work mode makes the contacting points of these linking parts wear out causing the restriction work mode to become unstable. And furthermore, as the electromagnet operator 32 is required to be activated electrically during operation so that the linking part 32a may be apart from the linking part 32, there is a slight increase in power consumption.
In the example shown in FIG. 1C, there is no problem regarding either power consumption or mechanical wearing. In releasing the arm 4 from the restriction state, the piece 35 is required to be removed from the permanent magnet 34 by making the actuator 5 generate a large force. Thus, the arm 4 in a release work mode tends to rebound after colliding with a stopper or the like provided on the side of the magnet 35. As a result, the leaf spring 3a vibrates so that the head 3 can make contact with the surface of the disc 1 to scratch it. In order and avoid such failures, there is no effective way except to reduce the restriction force developed between the permanent magnet 34 and the piece 35. Thus, under this situation, a stable restriction work mode can not be established.